A small base station generally called a femto cell/pico cell is inexpensive and may provide a high-speed data service. In addition, because the small base station can provide a high quality service to a user located in a shadow area, it may be an attractive solution to a mobile communication service provider or users.
The femto/pico cell is divided into an open access mode and a closed access mode depending on an access policy. The open access mode allows all subscribers who have subscribed to a service of a service provider to access the cell within a radius of a base station. The closed access mode does not allow all subscribers' access but allows an access to only a specific user group. In addition, a hybrid access mode supports these two modes.
When femto/pico cells are installed inside a macro cell region and operated, the femto/pico cells need to be turned off for interference reduction and conserving power as needed.
More particularly, because an interference that a femto/pico cell causes to a macro cell has an influence on the performance of the existing macro cell, the interference should be minimized. One of methods for reducing the interference of a femto/pico cell is to change the state of the femto/pico cell to a turn-off state in which the femto/pico cell suspends signal transmission when needed. The femto/pico cell has a relatively small cell size, such that a situation in which a terminal that belongs to the femto/pico cell does not exist frequently occurs.
Therefore, when a terminal to which the femto/pico base station should provide a service does not exist, when the femto/pico base station suspends signal transmission, an interference to the macro cell does not occur. However, in this situation, even when a new terminal enters the femto/pico cell region, the femto/pico cell cannot automatically wake up.
More particularly, because the femto/pico cell base station does not send any signal, a terminal cannot recognize that it is in the femto/pico cell region, and cannot recognize the femto/pico cell region to which the terminal belongs.